Field cress might replace soy in animal feed

Large quantities of soy are used as animal feed. This choice is often criticised, notably because growing this crop boosts deforestation of the Amazon region. Researchers are currently investigating whether the humble field cress (Lepidium campestre) plant can become a Swedish-grown alternative, which a Mistra Biotech study shows is entirely possible.

There are hopes that field cress may become a new commercial oil crop in Sweden and other countries with a cold climate. The main idea is for the oil to be used for food and biodiesel, and as a raw material in the chemical industry.

It has taken time to improve field cress, breeding it from a wild plant that grows sparingly on road verges and embankments to a cultivable crop. To date, research scientists have spent 20 years on the project. In this time major advances have been made, but further breeding remains necessary. For example, the plant’s capacity to retain its seeds until harvest, instead of often spreading them to the wind as it does now, needs improving. For the past eight years, the work has been carried out within the framework of Mistra Biotech.

In recent years, oilseed cake — a protein-rich residue left after the oil in field-cress seeds has been squeezed out — has aroused the scientists’ interest. They are interested in whether the oilseed cake can be used as animal feed. In a pilot project, Emma Ivarsson of the Department of Animal Nutrition and Management at the Swedish University of Agricultural Sciences (SLU) in Uppsala has examined both the pros and cons of field cress as feed.

The eight pigs in the study received their usual feed mixed with 4, 8 or 12 per cent field cress. First, whether the pigs liked the flavour was tested. In this respect, no differences were found among the different varieties or compared with the control feed.

The next step was to investigate the plant’s digestibility, which is crucial for whether the pigs absorb the nutrients contained in the feed.

‘Field cress proved to be more difficult to break down compared with traditional feed, the reason being that the oilseed cake contains more fibre. This means that field cress shouldn’t be given in excessive concentrations to growing animals with high nutritional needs,’ Ivarsson says.

On the other hand, its relatively low digestibility should not be a problem for sows or ruminants. However, this was not examined in this study.

One concern with field cress is that the plant contains relatively high levels of the unhealthy substance glucosinolates.

‘In the study, we saw no signs of ill-health in the pigs. To know for sure, we’d need to investigate the effects over a long period. But we believe there’s no problem in giving pigs oilseed cake from field cress at the mixing levels we’ve investigated.’

Seed capsules of rape, which are also used as animal feed, have had the same problem of high glucosinolate levels, but these have been reduced by intensive breeding efforts.

‘The hope is that the scientists can cut the levels, although glucosinolates in field cress don’t seem to be as toxic as in oilseed rape.’

Ivarsson thinks finding alternatives to the soy currently imported for use in animal feed is vitally important. Given, too, that not enough oilseed rape is grown in Sweden for it to be a significant substitute feed, there is great value in also using field cress as feed.

Field cress is a plant with undistinguished flowers and soft, greyish, hairy leaves. Found rarely in southern and central Sweden, it tends to grow on road verges and on embankments.

For more than 20 years, researchers have been trying to domesticate this biennial oil plant. In recent years, this work has taken place within the Mistra Biotech research programme. The hope is that this plant’s winter-hardiness will make it an interesting alternative to oilseed rape. According to estimates, harvests of up to five tonnes per hectare will be attainable, but much remains to be done first. The researchers’ aims include raising the oil content and changing the composition of fatty acids. The fact that field cress contains toxic glucosinolates is another concern, but scientists at SLU in Alnarp are trying to manage this problem by stopping the substance from being transported from the plant to its seeds.

In an initial stage, the scientists are trying to use genetic engineering to obtain a plant with the desired properties. After that, with the genetically modified variant as a model, they will attempt to achieve the same results by means of traditional plant breeding, enabling the plant later to be commercialised in Europe.

Since field cress is biennial, it can be undersown with one of the Nordic region’s common cereal varieties. When these are harvested, the field cress keeps growing for another year. This reduces nutrient leaching and the need for tillage, and helps to make agriculture sustainable.